The account https://twitter.com/dlang_org looks like D-related, but the
posts are mostly unrelated to the language. Does anyone know the owner
of the account?

Don't know who it is, but I think you or Walter would be in your right to
request it is removed.
It looks to me like some sort of automated bot that tweets about
"programming" related news articles. But it's not even spam, it has no
links. Just random headlines...
It has 1700 followers! more than half of D_Programming.
-Steve